1. Technical Field
The present invention relates to a projection system, and more particularly to a technology of the projection system used for presentation or the like, and relates to a projector use in the projection system.
2. Related Art
Recently, a technology of front-projection-type projector which can perform so-called close projection capable of displaying a large screen from a short projection distance has been proposed. The close projection can be achieved by widening angle of light to be projected. The close projection requires only narrow space for displaying a large screen. Moreover, the projector does not become an obstacle for image viewing when light is diagonally projected from a position close to a light receiving surface. Currently, a technology of close projection has been proposed in JP-A-2002-40326, for example. According to the method disclosed in JP-A-2002-40326, angle is widened by using a reflection-type image forming system as a combination of a plurality of reflection mirrors.
When light is diagonally projected from a position close to the light receiving surface, the light is not easily blocked compared with a related-art projector which is disposed at a position away from and opposed to the light receiving surface. For example, in case of the situation that a person giving an explanation uses display produced by the projector capable of performing close projection, shadow of the person on the light receiving surface can be reduced even when the person stands at a position close enough to directly touch the light receiving surface by hand or indirectly touch the surface with a pointing bar. Thus, the projector capable of performing close projection is appropriate for presentation.
During presentation, for example, the person gives an explanation while touching the light receiving surface by hand or pointing bar in some cases. When light from the projector is blocked by the contact between an object such as hand and pointing bar and the light receiving surface or by bringing the object close to the light receiving surface to such an extent as to contact the surface, shadow of the object is produced on the light receiving surface. When light greatly inclined to the normal line of the light receiving surface and entering the light receiving surface is blocked, longer shadow than that produced by light less inclined to the normal line of the light receiving surface is produced. In case of close projection, therefore, there is a possibility that the long shadow produced on the light receiving surface causes adverse effect on image display.